from Western Australia. 387 



periphery broad, flattened, its width about one-half that of the lateral area, its 

 margins subangular. Umbilicus of moderate size, deep, with steep sides, exposing 

 a portion of the inner whorls ; margin rounded. Siphuncle not seen. Chambers 

 rather deep, about two-fifths of the corresponding height (breadth) of the whorl in 

 depth at the periphery; suture-line forming a sigmoidal curve on the side, its 

 direction on the periphery not seen. Test covered with numerous subregular longi- 

 tudinal ridges, about one-twelfth of an inch apart where the height of the whorl is 

 three inches, and one-tenth of an inch apart where the whorl reaches five inches 

 in height; between each pair of ridges lie five or six very fine thread-like wavy 

 longitudinal lines. 

 Dimensions : — - 



Diameter of shell 8^ inches (216 mm.) 



Height of outer whorl 5 ,, (127 ,, ) 



Height of outer whorl above preceding whorl about 3J ,, (89 ,, ) 



Thickness of outer whorl about 4^ ,, (114-0 ,, ) 



Width of umbilicus f „ (19 ,, ) 



Depth of chamber at periphery where whorl has a height 



of4*inches 1| ,, (41-5 ,, ) 



Bemarks. — This species is represented by only one example, which 

 consists of the septate portion of the shell and the base of the body- 

 chamber. One side is much abraded, but the periphery and the 

 other side are well preserved, portions of the shell remaining on 

 the umbilical and peripheral regions and on parts of the lateral area, 

 sufficient to show that the ornamentation of the test extended over 

 the whole of the sides ; the greater part of the lateral area is denuded 

 of the test, and shows the course of the suture-lines. The position 

 of the siphuncle is not seen. 



The collection of Western Australian fossils in the Bath Museum 

 contains a Nautilus, which, though much worn, has a small fragment 

 of the test preserved near the extremity of the shell and close to the 

 periphery (hence probably assigned by Moore to N. semistriatus, 

 d'Orb.), that enables the writer to identify it with the present species. 

 The dimensions of the specimen are as follows : — 



Diameter of shell 120 mm. 



Height of outer whorl 77 ,, 



Height of outer whorl above preceding whorl 51 ,, 



Thickness of outer whorl (shell crushed on one side) ...about 68 ,, 



Width of umbilicus (obscured by matrix) about 14 ,, 



Depth of chamber where shell has a diameter of 95 mm. ... 21 ,, 



This specimen does not show the position of the siphuncle. 



Affinities and differences. — The species of Mesozoic Nautili which 

 have hitherto been identified from Australia are Nautilus simintus ? ^ 

 and Nautilus semistriatus,^ both from Western Australia. Nautilus 

 subsinuatus, d'Orbigny^ (=Nautilus sinuatus, J. Sowerby *) is dis- 

 tinguished from the present species by its more compressed form 

 and the narrower and deeper lateral sinus of its suture-line. In 

 Nautilus semistriatus, d'Orbigny,^ the longitudinal ornaments do not 



1 W. B. Clarke, " On Marine Fossiliferous Secondary Formations in Australia," 

 Quart. Journ. Geol. Soc. vol. xxiii. (1867), p. 8. 



^ C. Moore, "Australian Mesozoic Geology and Palaeontology," Hid. vol. xxvi. 

 (1870), pp. 230-232. 



3 Prod, de Paleont. Stratigr. vol. i. (1850), p. 260. 



* Min. Con. vol. ii. p. 213, pi. cxciv. 1818. This name was preoccupied by 

 Fichtel and Moll in 1803, and hence altered by d'Orbigny to suhsinuatus. 



5 Pal. Fran9. Terr. Jur. vol. i. 1842, p. 149, pi. xxvi. 



